1. Field of the Invention
The present invention relates to an information processing technology, and in particular, to an information processing apparatus which performs data transmission via a bus while processing a plurality of tasks in parallel, and an access control method thereof.
2. Description of the Related Art
With the significant progress of information processing technology in recent years, information processing apparatuses that perform high-speed operations are becoming increasingly common. As processors have improved in computing speed and the like, information processing apparatuses and electronic devices currently in the mainstream are capable of processing a plurality of applications or tasks in parallel. For parallel processing, it is typically the case that tasks are time-divided for the purpose of allocating the processing time of a processor. Virtual memory areas are also allocated to respective applications. The allocation of the processing time, memory capacity, and the like to a plurality of tasks is performed by an operating system (hereinafter, abbreviated as OS). The OS also exercises exclusive control, synchronous control, and the like over accesses among the processor, memory, and I/O devices when processing a plurality of tasks.
Now, the increase in the speed of processors and the introduction of virtual memory systems have made it possible to process a large volume of data at high speed, with an emerging problem in the efficiency of use of bus bandwidths intended for data transmission. Take, for example, the case of executing a plurality of applications including one to which real-time responses are essential, such as a game which displays three-dimensional moving graphics images. Even if the image processing is performed smoothly, a situation may occur in which the outputting of image data of the game is hindered because other applications are transmitting large volumes of data through a bus.
One of the approaches that has been proposed to solve this problem is a technique of granting permission to use the bus at higher frequencies to tasks of higher priority (for example, see U.S. Patent Application Publication No. US 2005/0138621). In this case, before issuance of data transmission requests, processing for acquiring issuance permission, called a “token,” is performed. Since tokens are granted up to rates that are determined in advance for respective source units of data transmission requests, tasks of lower priority are provided with lower rates of data transfer so as to reduce their impact on other processing tasks.
In the meantime, demands for faster processing are ever increasing, creating a desire for technology that is capable of achieving high speeds at lower cost without an increase in implementation area. The inventors have recognized, however, that even with the foregoing technology for using bus bandwidths efficiently, for example, some latency can occur from the processing of granting tokens with a possible delay in processing time.